What distinguishes a PDU1 PGN from a PDU2 PGN, and how does that affect addressing?

• A. PDU1 uses the PS field to address a specific destination (destination-addressed).
• B. PDU1 is a broadcast message; PDU2 addresses a specific device using a destination address.
• C. PDU1 messages are only used for engine data; PDU2 messages are for navigation data.
• D. PDU1 uses a different protocol than PDU2 but both address destinations.

Answer: (A)

On NMEA 2000, the way a message is addressed depends on the PDU format. For a PDU1 PGN, the PF field is less than 240, and the PS field carries the destination address, so the message is targeted at a single device—the data is meant for one specific node on the bus. The payload is structured so seven data bytes hold the actual data, and the eighth slot is the destination address, enabling precise delivery.

For a PDU2 PGN, the PF is 240 or greater, and the PS field is used as a group function rather than a destination. There is no single recipient; the message is broadcast to all devices that listen for that PGN, and each device uses its own filtering to decide whether to act on it.

So the key distinction is how the PS field is used: destination addressing in PDU1 versus broadcast/group addressing in PDU2. The other statements either flip which format is broadcast versus targeted or introduce elements (like different data domains or protocols) that don't apply.